Aquatic Environment and Biodiversity Annual Review 2012

4.4.4. Sources of uncertainty
AEBAR 2012: Protected species: Fur seals
Any measure of the effect of NZ fur seal mortality from commercial fisheries on NZ fur seal
populations requires adequate information on the size of the populations at different colonies.
Although there is reasonable information about where the main NZ fur seal breeding colonies exist,
the size and dynamics of the overall populations are poorly understood. At present, the main sources
of uncertainty are the lack of consistent data on: abundance by colony and in total; population
demographic parameters; and at-sea distribution (which would ideally be available at the level of a
colony or wider geographic area where several colonies are close together) (Baird 2011). Collation
and analysis of existing data, such as that for the west coast South Island, would fill some of these
gaps; there is a 20-year time series of pup production from three west coast South Island colonies, a
reasonably long data series from the Otago Peninsula, and another from Kaikoura. Maximum benefit
could be gained through the use of all available data, as shown by the monitoring of certain colonies
of NZ fur seals in Australia to provide a measure of overall population stability (see Shaughnessy et
al. 1994, Goldsworthy et al. 2003).
Fur seals may forage in waters near a colony or haulout, or may range widely, depending on the sex,
age, and individual preferences of the animal (Baird 2011). It is not known whether the NZ fur seals
around a fishing vessel are from colonies nearby. Some genetic work is proposed to test the potential
to differentiate between colonies so that in the future NZ fur seals drowned by fishing gear may be
identified as being from a certain colony (Robertson and Gemmell 2005).
The low to moderate levels of observer coverage in some fishery-area strata adds uncertainty to the
total estimated captures. However, the main source of uncertainty in the level of bycatch is the paucity
of information from the inshore fishing fleets using a variety of methods. Recent increases in observer
coverage enabled fur seal capture estimates to include inshore fishing effort. Further increases in
coverage, particularly for inshore fisheries, would provide better data on the life stage, sex, and size of
captured animals, as well as samples for fatty acid or stable isotope analysis to assess diet and to
determine provenance. Information on the aspects of fishing operations that lead to capture in inshore
fisheries would also be useful to design mitigation.
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